The present invention relates to novel bluish green emitting fluorescent materials of alkaline earth metal boron phosphates activated by a divalent europium compound.
In the specification, the fluorescent material means "phosphor" and the boron phosphate means "borate phosphate".
Heretofore, it has been well-known that strontium-magnesium phosphate activated with copper (Sr,Mg).sub.3 (PO.sub.4).sub.2 :Cu and calcium halophosphate activated by antimony Ca.sub.10 (PO.sub.4).sub.6 (F,Cl).sub.2 :Sb are used as typical fluorescent material emitting in bluish green wavelength region under exciting it by ultraviolet radiation or cathode radiation.
However, these known fluorescent materials have disadvantages to be unsatisfactory from the practical viewpoints.
When the flourescent material of a phosphate activated by copper is used for a low pressure or high pressure mercury discharge lamp, it is difficult to avoid a trouble of a serious decrease of luminous output because the activator of copper is oxidized by heating (such as 600.degree. C.) in a baking step (lehring) for the fluorescent material in the preparation of a flurorescent lamp.
The fluorescent material of a halophosphate activated by antimony has wide luminous regions so as to emit an emission energy even in near-ultraviolet wavelength region as invisible region. Accordingly, it is difficult to obtain satisfactory luminous efficiency by using it in a discharge lamp for lightening.